Modern transmission networks are composed of a number of interconnected network elements like terminal multiplexers, add/drop multiplexers, crossconnects, and regenerators. Examples of transmission networks are synchronous transmission networks known as SDH or SONET (G.707 October 2000) and optical transport networks (OTN, G.709 February 2001). Such networks serve for the transport of tributary user signals in multiplexed form. ITU-T recommendations G.707 (October 2000) and G.709 (February 2001) are incorporated by reference herein.
SDH technology relies basically on time-division multiplexing while OTN uses basically wavelength-division multiplexing as well as time-division multiplexing. Mappings are provided which allow the transport of SDH type transmission signals in multiplex units of OTN.
Future transmission networks will consist of sub-networks using SDH technology and other sub-networks using OTN technology. Sub-networks using different transmission technologies will be interconnected at “interconnection nodes”, containing both SDH and OTN functionality.
A challenge in such heterogeneous future transmission networks will be the management and control of the network.
An SDH network is today controlled by its own central network management system. Similar dedicated management systems will also be provided for OTNs. Such management systems are also referred to as operations system (OS).
Both SDH and OTN allow to transport management information in the overhead of transmitted communications signals. In SDH, bytes D1 to D12, referred to as data communication channels (DCC), in the section overhead (SOH) of transmitted signals are reserved for the transport of management information messages. Likewise, the OTN standards provide bytes GCC0 to GCC2, which are termed general communication channels, in the OTU/ODU overhead (OTU: optical channel transport unit, ODU: optical channel data unit).
A problem exists if an SDH sub-network has to be controlled but is reachable from the operations system only via an OTN sub-network, or vice versa. The interconnection node then has to mediate the management information between the SDH and the OTN sub-networks.
A solution to this problem would be the use of two separate network elements (NEs) in the interconnection node, one for SDH and one for OTN, and to pass the management information between these two NEs via dedicated management interfaces. This encompasses, however, the drawback that the management information has to pass through the dedicated external management interfaces of the two NEs in the interconnection nodes and through corresponding separate routing engines for DCC and for GCC. This is however, costly and complex and would increase the delay of management information on its way through the network.
It is thus an object of the present invention to provide a method and corresponding network element which allows the control of heterogeneous transmission networks by an central management system.